Finland, which shares a 1,300km (800 miles) border with Russia, has seen public opinion to join Nato change dramatically since Russia’s “special military operation” began in Ukraine in February.
“We hope that the national steps still needed to make this decision will be taken rapidly within the next few days,” the Finnish leaders said.
Sweden’s ruling Social Democrats are expected to decide on Sunday whether to overturn decades of opposition to Nato membership, a move that would almost certainly lead to Stockholm also asking to join the 30-nation alliance. However, Moscow has warned it could deploy nuclear weapons and hypersonic missiles in the European exclave of Kaliningrad if the two countries pursue their applications.
Despite the warnings, Nato is confident security concerns can be tackled in the interim while the UK on Wednesday signed a security pact with Finland and Sweden agreeing to provide military protection to the nations if they are attacked.
But with Russia’s explicit threats to Finland and Sweden and its proximity to Moscow, why would the two Nordic nations want to join Nato.
Why are Sweden and Finland not current Nato members?
Finland has a violent history with Russia having fought two wars against it before eventually gaining independence from it in 1917. Finland later signed an Agreement of Friendship, Cooperation and Mutual Assistance with Russia agreeing to isolate itself militarily from western Europe while remaining politically and economically dependent on Moscow.
However, the fall of the Soviet Union following the end of the Cold War gave Finland a chance to step out of Russia’s shadow, but still maintained friendly relations with Moscow.
Sweden on the other hand has not fought a war for 200 years and post-war foreign policy has focused on supporting democracy internationally, multilateral dialogue and nuclear disarmament.
It ran down its military after the Cold War, hoping in the event of any conflict it could delay a Russian advance until help arrived. President Putin's offensive against Ukraine, however, has made a guarantee of aid much more appealing.
However, many on the left in Sweden remain suspicious of the US security agenda and Nato, which ultimately relies on the deterrence provided by the US nuclear arsenal.
Both Sweden and Finland have drawn ever closer to Nato in recent years, exchanging intelligence and participating in alliance exercises, in response to an increasingly belligerent Russia. Joining the alliance would bring Sweden and Finland under the umbrella of Article 5, which guarantees that an attack on one Nato ally is an attack on all
Is Finland and Sweden Nato membership supported?
Polls show a substantial majority of Swedes back joining Nato with support running just above 60 per cent in the latest poll and there is a majority in parliament in support of an application.
Sweden's Social Democrats - the biggest party, which has held power for most of the last century - has long championed military non-alignment but has been reviewing its objections with a decision on whether to join now due on Sunday. The party is widely expected to back membership.
The Swedish Left Party - formerly the communist party - remains against membership, as does the Green Party.
Meanwhile in Finland opinion polls show support for membership in Finland has run even stronger than in Sweden, with many Finns mindful of the long land border shared with Russia, while support in parliament for an application is also broad.
The Finnish parliament's defence committee said this week that joining Nato was the best option to guarantee national security.
How soon could Finland and Sweden join Nato?
Finland has a Nato “option” which means its law mandates that it applies to join the military alliance if its security situation deteriorates. Sweden’s parliament, meanwhile, will present a new security policy review on Friday but is not expected to contain an explicit recommendation concerning Nato.
Sweden's ruling Social Democrats are expected to decide on Sunday whether to overturn decades of opposition to Nato membership, a move that would almost certainly lead to Sweden also asking to join the 30-nation alliance.
Nato secretary-general Jens Stoltenberg said Finland’s membership would “strengthen” the western military alliance and that the process would be “smooth and swift.”